[NoStatePrefetch] Add UMA histogram to count prefetch requests

chrome/browser/prerender/prerender_histograms.h

Index: chrome/browser/prerender/prerender_histograms.h
diff --git a/chrome/browser/prerender/prerender_histograms.h b/chrome/browser/prerender/prerender_histograms.h
index f48c850b7569d0b989d849fd894f153c621d567f..7631af20b5b39daa88e24de110b924cf436726db 100644
--- a/chrome/browser/prerender/prerender_histograms.h
+++ b/chrome/browser/prerender/prerender_histograms.h
@@ -107,6 +107,11 @@ class PrerenderHistograms {
                           int64_t prerender_bytes,
                           int64_t profile_bytes);
 
+  // Record resources loaded by NoStatePrefetch.
+  void RecordResourcePrefetch(Origin origin,
+                              bool is_main_resource,
+                              bool is_no_store);
+
  private:
   base::TimeTicks GetCurrentTimeTicks() const;